Since 2010 there have been several global and regional targets and initiatives to halt and reverse land degradation and restore degraded land; the most recent being the 2030 Agenda for Sustainable Development and the Sustainable Development Goals (SDGs). SDG indicator 15.3.1, the proportion of land that is degraded over total land area, is assessed in terms of change in three sub-indicators: land cover, land productivity and carbon stocks. Each of these sub-indicators represents a unique perspective on the manifestation and assessment of land degradation. Soil organic carbon (C) is the current metric for assessing the carbon stocks sub-indicator. Good practice guidance (GPG) has recently been developed to assist countries to report on SDG indicator 15.3.1, and support countries to achieve their targets for reducing degradation.

Without being prescriptive about the sources of data, the GPG aims to ensure technical soundness and consistency in estimation methods as well as comparability of results across countries and over time. The approach used to quantify change in soil organic C stocks will vary depending on the availability of country-specific data and capability. Key challenges include the establishment of appropriate baselines and methods for determination of significant change in soil organic C stocks. The latter is further complicated by the typically slow rate of change in soil organic C in relation to indicator reporting periods. This paper presents some of the key methodological details of the GPG for assessing soil organic C stocks and describes considerations that may assist in national scale monitoring of soil organic C in order to implement national reporting against SDG indicator 15.3.1.